The present invention relates to a DCxe2x80x94DC converter and a semiconductor integrated circuit device for a DCxe2x80x94DC converter, and, more particularly, to a DCxe2x80x94DC converter which is used as a power supply for a portable electronic apparatus.
A DCxe2x80x94DC converter is installed in a portable electronic apparatus, such as a notebook type personal computer. The DCxe2x80x94DC converter supplies DC power, supplied from an external AC adapter, to internal circuits of an electronic apparatus and charges a battery equipped as an auxiliary power supply.
To operate the AC adapter stably and safely, the DCxe2x80x94DC converter is designed in such a way that the sum of the current consumed by the internal circuits and the charge current of the battery becomes smaller than the current supplying capacity of the AC adapter. When AC adapters of different current supplying capacities are to be used, it is necessary to use the current supplying capacity of each AC adapter to the full.
FIG. 1 is a schematic circuit diagram of a DCxe2x80x94DC converter 1 according to first prior art. The DCxe2x80x94DC converter 1 has a control unit 20 constructed on a single-chip semiconductor substrate and a plurality of external devices.
The output signal, SG1, of the control unit 20 is supplied to the gate of a switching transistor 3 which is preferably comprised of a P channel MOS transistor. An input voltage Vin (the output voltage of an AC adapter 4) is applied via a resistor R1 to the source of the switching transistor 3 from the AC adapter 4 connected to an electronic apparatus.
The input voltage Vin is applied to a first output terminal EX1 via the resistor R1 and a diode D1. An output voltage Vout1 is supplied to the internal circuits of the electronic apparatus from the first output terminal EX1.
The drain of the switching transistor 3 is connected to a second output terminal EX2 via an output coil 5 and a resistor R2. The second output terminal EX2 is connected to a battery BT and connected to the first output terminal EX1 via a diode D2. A charge voltage Vout2 of the battery BT is output from the second output terminal EX2.
The drain of the switching transistor 3 is also connected to the cathode of a flywheel diode 6 whose anode is connected to a ground GND. The node between the output coil 5 and the resistor R2 is connected to the ground GND via a capacitor 7. The output coil 5 and capacitor 7 constitute a smoothing circuit which smoothes the output voltage Vout2.
The control unit 20 includes first and second current detectors 8 and 9, first to third differential voltage amplification circuits 10, 11 and 12, a PWM comparison circuit 13, an oscillation circuit 14 and an output circuit 15.
The first current detector 8 has two input terminals to which the voltage between the terminals of the resistor R1 is supplied. The output terminal of the first current detector 8 is connected to the inverting input terminal of the first differential voltage amplification circuit 10. The current detector 8 amplifies the voltage between the terminals of the resistor R1, thereby generating an output signal SG2, and sends the output signal SG2 to the first differential voltage amplification circuit 10.
The first differential voltage amplification circuit 10 amplifies a differential voltage between the voltage of the output signal SG2 and a reference voltage (first threshold value) Vref1 supplied to the non-inverting input terminal of the differential voltage amplification circuit 10, generating an output signal SG3. The differential voltage amplification circuit 10 sends the output signal SG3 to the PWM comparison circuit 13.
The second current detector 9 has two input terminals to which the voltage between the terminals of the resistor R2 is supplied. The output terminal of the second current detector 9 is connected to the inverting input terminal of the second differential voltage amplification circuit 11. The current detector 9 amplifies the voltage between the terminals of the resistor R2, thereby generating an output signal SG4. The current detector 9 sends the output signal SG4 to the second differential voltage amplification circuit 11.
The second differential voltage amplification circuit 11 amplifies a differential voltage between the voltage of the output signal SG4 from the second current detector 9 and a reference voltage (second threshold value) Vref2 supplied to the non-inverting input terminal of the differential voltage amplification circuit 10, generating an output signal SG5. The differential voltage amplification circuit 11 sends the output signal SG5 to the PWM comparison circuit 13.
The charge voltage Vout2 is supplied to the inverting input terminal of the third differential voltage amplification circuit 12. The differential voltage amplification circuit 12 amplifies a differential voltage between the voltage of the charge voltage Vout2 and a reference voltage (third threshold value) Vref3 supplied to the non-inverting input terminal of the differential voltage amplification circuit 12, generating an output signal SG6. The differential voltage amplification circuit 12 sends the output signal SG6 to the PWM comparison circuit 13.
The output signals SG3, SG5 and SG6 of the first to third differential voltage amplification circuits 10, 11 and 12 are supplied to the non-inverting input terminal of the PWM comparison circuit 13. The oscillation circuit 14 supplies the inverting input terminal of the PWM comparison circuit 13 with a triangular signal SG7 having a predetermined frequency.
The PWM comparison circuit 13 compares the triangular signal SG7 with one of the output signals SG3, SG5 and SG6 of the first to third differential voltage amplification circuits 10, 11 and 12 that has the lowest voltage. The PWM comparison circuit 13 outputs an L-level output signal SG8 in a period where the voltage of the triangular signal SG7 is higher than the output signal SG3, SG5 or SG6, and outputs an H-level output signal SG8 in a period where the voltage of the triangular signal SG7 is lower than the output signal SG3, SG5 or SG6.
The output signal SG8 of the PWM comparison circuit 13 is supplied to the output circuit 15. The output circuit 15 supplies the gate of the switching transistor 3 with the output signal SG1, as a duty control signal, which inverts the output signal SG8 of the PWM comparison circuit 13. Therefore, the switching transistor 3 is turned off when the duty control signal SG1 has an H level and is turned on when the signal SG1 has an L level.
In the DCxe2x80x94DC converter 1, as the input voltage Vin is supplied from the AC adapter 4, the output voltage Vout1 and a circuit current I1 are supplied to the internal circuits from the first output terminal EX1. The switching transistor 3 repeats the alternate ON action and OFF action in accordance with the duty control signal SG1 output from the control unit 20. As a result, a charge current IB is supplied to the battery BT from the second output terminal EX2.
In such an operation mode, as the input current Iin (I1+IB) from the AC adapter 4 increases, the voltage between the terminals of the resistor R1 increases so that the voltage of the output signal SG2 of the first current detector 8 rises. As a result, the voltage of the output signal SG3 of the first differential voltage amplification circuit 10 drops. When the voltage of the output signal SG3 becomes lower than the voltages of the output signals SG5 and SG6, the L-level duration of the output signal SG8 of the PWM comparison circuit 13 becomes longer. Consequently, the L-level duration of the duty control signal SG1 becomes shorter, thus making the ON time of the switching transistor 3 shorter. This reduces the charge current IB of the battery BT.
As the input current Iin decreases, on the other hand, the voltage between the terminals of the resistor R1 decreases so that the voltage of the output signal SG2 of the first current detector 8 falls. As a result, the voltage of the output signal SG3 of the first differential voltage amplification circuit 10 rises. When the voltage of the output signal SG3 becomes lower than the voltages of the output signals SG5 and SG6, the L-level duration of the output signal SG8 of the PWM comparison circuit 13 becomes shorter. Consequently, the L-level duration of the duty control signal SG1 becomes longer, thus making the ON time of the switching transistor 3 longer. This increases the charge current IB of the battery BT.
When the voltage of the output signal SG3 of the first differential voltage amplification circuit 10 is higher than the voltages of the output signals SG5 and SG6 of the other differential voltage amplification circuits 11 and 12, the ON time of the switching transistor 3 is controlled in accordance with either the output signal SG5 or output signal SG6.
The above operation controls the output signal SG2 of the first current detector 8 in such a manner that the output signal SG2 converges to the reference voltage Verf1. That is, the input current Iin is so controlled as to fall within the range of the current supplying capacity of the AC adapter 4.
As the charge current IB of the battery BT increases, thus increasing the voltage between the terminals of the resistor R2, the voltage of the output signal SG4 of the second current detector 9 rises. This reduces the voltage of the output signal SG5 of the second differential voltage amplification circuit 11. When the voltage of the output signal SG5 becomes lower than the voltages of the output signals SG3 and SG6, the L-level duration of the output signal SG8 of the PWM comparison circuit 13 becomes longer. Consequently, the L-level duration of the duty control signal SG1 becomes shorter. This makes the ON time of the switching transistor 3 shorter, thus reducing the charge current IB.
As the charge current IB decreases, the voltage between the terminals of the resistor R2 falls, thus reducing the voltage of the output signal SG4 of the second current detector 9. As a result, the voltage of the output signal SG5 of the second differential voltage amplification circuit 11 rises. When the voltage of the output signal SG5 becomes lower than the voltages of the output signals SG3 and SG6, the L-level duration of the output signal SG8 of the PWM comparison circuit 13 gets shorter. This lengthens the L-level duration of the duty control signal SG1. Consequently, the ON time of the switching transistor 3 becomes longer, thus increasing the charge current IB.
When the voltage of the output signal SG5 of the second differential voltage amplification circuit 11 is higher than the voltages of the output signals SG3 and SG6 of the other differential voltage amplification circuits 10 and 12, the ON time of the switching transistor 3 is controlled in accordance with either the output signal SG3 or output signal SG6.
The above operation controls the output signal SG4 of the second current detector 9 in such a manner that the output signal SG4 converges to the reference voltage Vref2. As a result, the charge current IB of the battery BT is controlled to such a given value as not to supply an overcurrent to the battery BT.
When the charge voltage Vout2 of the battery BT rises, the voltage of the output signal SG6 of the third differential voltage amplification circuit 12 falls. When the voltage of the output signal SG6 goes lower than the voltages of the output signals SG3 and SG5, the L-level duration of the output signal SG8 of the PWM comparison circuit 13 becomes longer. Consequently, the L-level duration of the duty control signal SG1 becomes shorter. This makes the ON time of the switching transistor 3 shorter, thereby reducing the charge current IB.
When the charge voltage Vout2 of the battery BT falls, on the other hand, the voltage of the output signal SG6 of the third differential voltage amplification circuit 12 rises. When the voltage of the output signal SG6 goes lower than the voltages of the output signals SG3 and SG5, the L-level duration of the output signal SG8 of the PWM comparison circuit 13 becomes shorter. This lengthens the L-level duration of the duty control signal SG1. As a result, the ON time of the switching transistor 3 becomes longer, thereby increasing the charge current IB.
When the voltage of the output signal SG6 of the third differential voltage amplification circuit 12 is higher than the voltages of the output signals SG3 and SG5 of the other differential voltage amplification circuits 10 and 11, the ON time of the switching transistor 3 is controlled in accordance with either the output signal SG3 or output signal SG5. This operation controls the charge voltage Vout2 of the battery BT in such a way that the charge voltage Vout2 converges to the reference voltage Vref3. That is, the charge voltage Vout2 is controlled to such a given value as not to excessively charge the battery BT.
In short, the first current detector 8 and the first differential voltage amplification circuit 10 in the DCxe2x80x94DC converter 1 control the input current Iin to lie within the range of the current supplying capacity of the AC adapter 4. Further, the second current detector 9 and the second differential voltage amplification circuit 11 control the charge current IB to a given value. The third differential voltage amplification circuit 12 controls the charge voltage Vout2 to a given value.
FIG. 2 is a schematic circuit diagram of a DCxe2x80x94DC converter 1A according to second prior art. The DCxe2x80x94DC converter 1A is the DCxe2x80x94DC converter 1 of the first prior art from which the resistor R1 and the first current detector 8 are removed. The output terminal of the AC adapter 4 is connected to the ground GND via resistors R3 and R4. A node N1 between the resistors R3 and R4 is connected to the inverting input terminal of the differential voltage amplification circuit 10.
In the DCxe2x80x94DC converter 1A, as the input current Iin increases over the current supplying capacity of the AC adapter 4, the input voltage Vin drops. The potential at the node N1 falls then, causing the voltage of the output signal SG3 of the first differential voltage amplification circuit 10 to drop. When the voltage of the output signal SG3 goes lower than the voltages of the output signals SG5 and SG6, the L-level duration of the output signal SG8 of the PWM comparison circuit 13 becomes longer. As a result, the L-level duration of the duty control signal SG1 becomes shorter, thus shortening the ON time of the switching transistor 3. This reduces the charge current IB of the battery BT. At this time, the input current Iin decreases too.
Through the above-described operation, the input current Iin is controlled to lie within the range of the current supplying capacity of the AC adapter 4. The second differential voltage amplification circuit 11 controls the charge current IB of the battery BT and the third differential voltage amplification circuit 12 controls the charge voltage Vout2 of the battery BT.
In FIG. 3, a characteristic line A shows the output voltage versus output current characteristic of the AC adapter 4 (the input voltage Vin versus input current Iin characteristic of the DCxe2x80x94DC converter 1). A characteristic line B shows the charge voltage Vout2 as a function of charge current IB characteristic of the DCxe2x80x94DC converter 1. The AC adapter 4 can change the output current while keeping the output voltage constant.
The AC adapter 4 has an overcurrent limiter which is activated to drop the input voltage Vin when the input current Iin reaches an upper operational limit P1. When the input current Iin reaches a maximum limit P2, the AC adapter 4 is shut down, thus stopping supplying the voltage Vin and the current Iin.
The DCxe2x80x94DC converter 1 charges the battery BT with the charge current IB while maintaining the constant charge voltage Vout2. An upper limit P3 of the charge current IB is set smaller than the upper limit P1 of the output current of the AC adapter 4.
FIG. 4 is a graph showing the relationship between the circuit current I1 and the charge current IB. Because sum of the circuit current I1 and the charge current IB is the input current Iin, as one of the circuit current I1 and the charge current IB increases, the other decreases, as shown in FIG. 4. The slopes of characteristic lines L1 and L2 that show the relationship varies in accordance with the current supplying capacity of the AC adapter 4.
In the first prior art, the input current Iin is set smaller than the upper operational limit P1 of the AC adapter 4. This is because when the input current Iin exceeds the current supplying capacity of the AC adapter 4, the AC adapter 4 is shut down.
One may change one AC adapter to another with a different current supplying capacity in accordance with the use condition; for example, a small-capacity AC adapter may be used in a portable mode while a large-capacity AC adapter may be used in a home or office. In this case, the upper limit of the input current Iin should be set relatively low so that a small-capacity AC adapter, if used, will not be shut down. With such a low upper limit set, the current supplying capacity of a large-capacity AC adapter, if used, cannot be used effectively.
In the second prior art, when the input current Iin exceeds the current supplying capacity of the AC adapter 4, the input voltage Vin drops. Therefore, the charge current IB is suppressed by detecting the drop of the input voltage Vin by the first differential voltage amplification circuit 10. Even if a plurality of AC adapters with different current supplying capacities are selectively changed from one to another to suit the occasion, the current supplying capacity of each AC adapter can be used fully.
With the use of a large-capacity AC adapter, it is not easy to secure the precision of the output voltage drooping characteristic when the output current that exceeds the current supplying capacity is output. The battery BT may therefore be charged with power greater than the allowable output power of the AC adapter. The AC adapter becomes hot in this case, disadvantageously.
Accordingly, it is an object of the present invention to provide a DCxe2x80x94DC converter which can permit AC adapters with different current supplying capacities to operate stably and can use the current supplying capacities to the full.
To achieve the above object, the present invention provides a DCxe2x80x94DC converter for generating a circuit current and charging a battery. The DCxe2x80x94DC converter includes a supply circuit for supplying the circuit current to internal circuits in accordance with an input current supplied from an external DC power supply, a charge circuit for receiving the input current and supplying a charge current to the battery, and a control unit, connected to the charge circuit, for controlling the charge current. The control unit includes a differential charge controller for comparing the input current with a first threshold value and controlling the charge current according to a result of that comparison, a charge current controller for comparing the charge current with a second threshold value and controlling the charge current according to a result of that comparison, a charge voltage controller for comparing a charge voltage of the battery with a third threshold value and controlling the charge current according to a result of that comparison, and a dynamic charge controller for comparing an input voltage from the external DC power supply with a fourth threshold value and controlling the charge current according to a result of that comparison.
The present invention further provides a semiconductor integrated circuit device for controlling a DCxe2x80x94DC converter. The DCxe2x80x94DC converter has a supply circuit for supplying a circuit current to internal circuits in accordance with an input current supplied from an external DC power supply and a charge circuit for supplying a battery with a charge current based on the input current. The device includes a control unit, connected to the charge circuit, for controlling the charge current. The control unit includes a differential charge controller for comparing the input current with a first threshold value and controlling the charge current according to a result of that comparison, a charge current controller for comparing the charge current with a second threshold value and controlling the charge current according to a result of that comparison, a charge voltage controller for comparing a charge voltage of the battery with a third threshold value and controlling the charge current according to a result of that comparison, and a dynamic charge controller for comparing an input voltage from the external DC power supply with a fourth threshold value and controlling the charge current according to a result of that comparison.